Selector



May 19, 1953' e. F. BELLAIRS arm.

" SELECTOR Filed Jan. 24, 1948 2 Sheets-Sheet 1 Patented May 19, 1953 SELECTOR Guy ffarington Bellairs, London, and John Charles Ireland, Tunbridge Wells. England, assignors to British Telecommunications Research Limited, Taplow, England, a British company Application January 24, 1948, Serial No. 4,146 In Great Britain January 27, 1947 (on. ant-r71) 6 Claims. 1

This invention relates to frequency selectors for use in automatic telecommunication systems.

It has been proposed in order to obtain any of a large number of possible frequencies-from a limited number of sources of waves of fixed frequencies to arrange such sources so as to supply waves of frequencies in sets, each set beingcomposed of a number of fixed frequencies equally spaced in arithmetical progression the frequency range of the second and any subsequent set being within the frequency spacing of the preceding set and to provide manually controlled means for selecting one frequency from each set and mixing such frequencies so as to obtain a resultant single combination frequency.

By the frequency range of a set is meant the difference between the highest and lowest frequencies in that set.

Two, three, four or more sets of frequencies may be made available.

One object ofthe invention is to provide a frequency generator which generates a wave having a frequency distinctive of a particular combination of signals transmitted thereto. Another object of the invention is to provide a frequency selector for use in a telecommunication system embodying a frequency generator as described above for producing a single combination Wave for the purpose of testing a communication channel in a transmission path and for conand over said transmission path.

In the case of the frequency selector being ar ranged to respond to three series of impulses three tenway switching or selecting devices are provided so that the final output will consist of a wave having any one of 1000 particular frequencies according to the various possible positions of the ten-way switches.

Furtherstages of selection may of course be added to the extent the frequency allocation permits.

The various sets of frequencies required might be derived from frequency multiplying devices locked to a common master oscillator.

The frequencies may be so chosen that unwanted modulation products do not appear in the output of the frequency generator.

The relation between a set of frequencies and the next set of lower frequency spacing is preferably thatthe spacing of the former exceeds the difference between the highest and lowest frequencies of, the latter by the frequency spacing of the latter. 5 r

'The invention more especially has application in telephone or like systems wherein each communication channel has associated a fixed frequency and in order to establish communication to a wanted communication channel it is necessary to provide a wave having the associated fixed frequency. Accordingto a further feature of the inven tion, in the case where a wanted station has associated a plurality of communication channels characterised by a progression of equally spaced frequencies it will be possible to arrange that should a frequency selected by the above method correspondto an engaged communication channel an appropriate change is automatically made in the selected frequency of one of the sets so that the frequency of another communication channel to the wanted station is provided and if this too is engaged the process may be repeated until a free communication channel is found or until all channels have been tasted and found busy.

Thus the impulse responsive means when operated may serve to initiate the operation of an automatically hunting frequency selector to establish communication with a selector channel independently of the impulse responsive means.

The invention will be better understood from the following description of methods of carrying it into elfect, described with reference to the accompanying drawings.

Fig. 1 shows circuit details of an important component of the invention which in itself is not broadly novel;

Fig; 2 shows theinvention as applied for use in a telephone system of the kind described in our c'opending application Serial No; 4,143, filed January 24, 1948.

In Fig. 1, two of the selected frequencies are obtained by setting the ten-point switches SI and S2 (for instance as described in connection with Figure 2) to appropriate positions each of the ten positions being supplied with a wave of discrete frequency, the frequencies of the ten waves connected to the ten positions of each switch forming a set of the nature previously described. The selected waves are fed. respecto the first control grid of a hexode valve mixer The present invention is illustrated in Fig. 2,

which figure is also shown in our copending application Serial No. 4,143, filed January .24, 1948, now Patent No. 2,607,853, issued August 19,1952, and is the circuit of an exchange-selector as suitable for use in a telecommunication system.

It is assumed that suitable trains of impulses are received by the relay AA over line T23 corresponding to the hundreds, tens and unitdigit of a wanted substation number. In thearrangement shown only the pulses corresponding to the hundred and tons digits will be utilised for providing a combination frequency and this frequency'will be variable bygathird stage offrequency selection which 'will Jae-a hunting stage. Such an arrangement'.- would--correspond-to a hypothetical system in which each subscriber had ten PBX lines.

1 Y In'Figure 2-the equipment shown 'n-thedotted rectangle DFG3 corresponds to thatshown'in Figure 1 by reference to which the corresponding components will be readily apparent.

When impulses are received, relay AA operates intermittently and completes at AA! a circuit for change-over relay CC and, the magnet MTT through the first wiper of a'steering switch SS in normal position. CC operates and holds up only during thetrainsofimpulses. At-CC I it completes the circuit for magnet-MS- of' steering switch SS. ;MTT.responds- -to the impulses and steps the wipers-of-the hundreds switch TTS in accordance with .thefirst;;digit dialled. 1 This switch may be a three bank rotary switch,:=the first wiper of which steps over ten contacts to each of which is connectedwne of the sets'of sources of waves having equally's'paced frequencies, which maybe as follows:

Home contact, disconnected. I Kilocycles 1st contact 24,000

2nd contact 24,800 3rd contact 25,600 4thcontact 8 26,400 5th contact 27,200 .6th contact 528,000 7th contact L 28,800 8th contact 29,600 9th contact 30,400 10th contact fI'he-secondwi per. moves over anloff normal contact strip, to provide..a homing circuit for the switch T'I'S. I i r I ...When the first series ofiimpulses ceas e the first wiper of TTS rests on a contactcorresponding to the first digit and relay CC releases shortly after, opening the circuit of MS at CC! to cause the wipers of the steering switch SS to advance one step so that the impulsing circuit is now connected to the magnet MT-of the thousands switch TS. The next series of impulses therefore operate MT and CC. Magnet M'I advances the wipers of the switch Ts to thqpositioncorresponding to the tens digit, MS being energised by contact CCI as before, The switch TS corresponds generally to the switch TTS but the frequencies respectively connected to the first bank contacts will be:

Home contact, disconnected.

1st contact Kilocycles 16,320

2nd contact 1 16,240 3rd contact 1 16,160 4th contact 16,080 5th contact 16,000 6th contact 15,920 7th contact .f 15,840 8th COIltaJQt i 15,760 "9th conta ct' 15,680 10thcontactl 15,600

At the end, of the second digit, MS releases and advances the switch SS to the third posischist-aria interrupt the impulsing circuit.

'The switches TTS and TS constitute with huntingcsyvitch HS, a decade frequency generator as previously described, so that frequencies selected. by. the. .left-harld .wiperslofHS. and TS .1. Kilocycles Home, or. 1st. contact 1 .1632 2nd contact 1624 3rd contact. 1616 4th contact ..16.08

5thcontact 1600 fithcontact' ..1592 7th contact 1584 When CC operated for? he'secondidigit; it completed at GCZ, f immediately 'the"wipers TS had left 'ther-normalpositionya circuit for slow release r'ela'y :Relay T on energising operates contactTl." so'fthat whenthe wipers of the's'witcli SS were stepped to."the'rthird -position" a circuit was completedfrom .the -mixer --M3D over 'Tl front contact,'*-contact" and wipe'r' of switch? SS in third'position :to the r'output-r ofwthe decade frequency generator thereby'completing a busy test circuit "from ."BPFSBfISS" in third position; Tl operated :..to'; MQDI' Consequently this i'b'usy test circuit onlya-becomes effective when'theree lay CC?:de=energisesr;.atethe end of the second digit: f *1 "iii? 3 111* "Theswitch HS has a frequency connected to the" normal contactwhich when'emixed with the frequencyiconnected up :by. TS; to-M3B "gives resultanfi-frequencies 10f which the sum frequency passes through BPE3AL.to-.:M3A-wheritmixes with; the frequency. i=flom switch "ITS sand the difference (say) 1 passesthrou'gh BPF3B to "the test circuit; this latter frequency is designed to correspond'ito; the first of the. selected group of carrier frequencieswhich lead to the wanted destination. 1 1 r It is-assumedi-thavthereare 'tencarrier frequencies in a group corresponding to the .capacity of the-switch-HS,,but of course there may be a difierent number if desired, provided that the whole range of carrier frequencies is no greater thamthe difference between 'the frequencies selected theiswitch TS. on succes- II'j l .1. 3;; 1 In Terminals T3A and B are multiplr her e ch n sel c s a er-e se ssteat able the sum and difference of the carrier frequency on T33 and the fixed frequency. If therefore the carrier frequency is present on T313 corresponding to the frequency applied to MED over the busy test circuit as described, i. e. the first of the selected group of carrier frequencies indicating that the communication channel first tested is busy there will be an output from M31) corresponding to the fixed frequency of oscilla tor FFO say 500 cycles which passing to detector D3A through the low pass filter LPF? will cause the relay GG to operate. Relay GG at quencies which are separated by amounts of one value/a second series of sources of fixed frequency waves, the sources of said second series being designed to supply waves having distinctive frequencies which are separated by amounts of another value, the amount between the lowest and highest frequency of said second series of sources being less than any amount separating the frequencies of said firstseries, wave mixing means, a first selecting device by which any one of said first series of sources may be connected to said mixing means,ya second selecting device by which any one of said second series of sources may be connected to said mixing mean-s, filter means for restricting ,the output from said mixer to a resultant wave" of a single frequency, which frequency is a distinctive combination of the'frequencies of the waves selected bysaid selecting devices and distinct from any of the frequencies of the first and second series of sources, means for con necting said resultant wave to said output terminals and control means operable over and contact GGI completes a'circuit for magnet MI-I through "its own interrupting contacts and a maintaining circuit for relay T at GG'J. The switch HS will therefore step and advance the wipers step-by-step until a carrier frequency is placed on the test circuit for which there is no corresponding frequency on the cable or line being tested.

If GG does not operate or after it has ceased to operate the circuit for relay T is opened and consequently this relay will release after a short interval and at contact Tl front contact transfers the frequency output of BPFi B from M313 to M36 and MBE rendering T333 busy with respect to the particular carrier frequency found and M3E effective to modulate audio frequency currents from T2B with the desired carrier frequency, while M3C is rendered effective to demodulate modulated carrier frequencies received over the selected channel.

The equipment can be restored by the closing of contact A4 of a relay A (not shown) whereupon magnet MB is operated over earth, contact A4 second wiper of HS in an off-normal position, magnet MI-I, battery. As magnet MB is self-interrupting it steps the first wiper of the switch HS round to its normal position, when the energising circuit for magnet MH is broken. When the first wiper of the switch HS reaches its normal position an energising circuit is closed for magnet MT, over; earth, contact A4, second wiper of HS in normal position, second wiper of TS in cff-normal position, magnet MT, battery. As magnet MT operates it disconnects its own circuit, stepping on of the wipers of TS combines until they reach the normal position. When the second wiper of TS reaches its normal position an energising circuit is closed for magnet MTT over earth, contact A4, second wiper of HS in normal position, second wiper of TS in normal position, second Wiper of TTS in ofi-normal positiorumagnet MTT, battery. MTT thereafter operates and restores until the wipers of switch TTS are restored to their normal position.

We claim: I

1. A frequency selector for use in a telecommunication system having input and output terminals, a variable frequency generator comprising a first series of sources of fixed frequency waves, the sources of said first series being designed to supply waves having distinctive frerectly'distinctive of the combination of signals received by said control means, means responresponsive to successive signals received at said input terminals by which the first and second selecting devices are operated in turn whereby thewave from the output to: said mixer is disive to signals received at said input terminals for successively operating said selecting devices,

testing means connected to said output termiv nals, means responsive to the cessation of said signals for applying the resultant wave derived from said frequency generator to said testing means, means forming part of said testing means adapted to respond if said resultant wave and a wave present on said output terminals cooperate to produce a Wave of a given frequency, and means operable on the cessation of said signals if said testing means fail to respond for causing said resultant wave to be applied to said output terminals to provide carrier currents for communication passing between said input and output terminals.

2. A frequency selector for use in a telecommunication system having input and output terminals, a variable frequency generator comprising a first series of sources of fixed frequency waves, the sources of said first series being designed to supply waves having distinctive frequencies which are separated by amounts of one value, a second series of sources of fixed frequency waves, the sources of said second series being designed to supply waves having distinctive frequencies which are separated by amounts of another value, the amount between the lowest and highest frequency of said second series of sources being less than any amount separating the frequencies of said first series, wave mixing means, a first selecting device by which any one of said first series of sources may be connected to said mixing means, a sec- 0nd selecting device by which any one of said second series of sources may be connected to said mixing means, filter means for restricting the output from said mixer to a resultant wave of a single frequency, which frequency is a distinctive combination of the frequencies of the .waves selected by said selecting devices and distinct from any of the frequencies of the first and second series of sources, means responsive to successive series of impulses received at said input terminals by which the first and second stepping switches are operated in turn to cause "sive assume was tdbe' generated-distinctive of thefedm inatmn 6*: numbers ofimpulses 'in each off saidserisfoffimpulses; testing-1 means con} nected said outputiltermina'ls, ineans' respon the cessatiOn- -ofsaid impulses form'applying theiesultant wave; derived{from said frequency g'e'rierator'jto said" testing meansfmean's forming part of said testing" means adapted to respond if said' resultant *waveamr "a wave pres ent on said output terminals cooperate-"to {pro-'- 'dtic a wave of" "iv'en 'freguency; and means operableon m senor; of; said impulses if said testing 'rnea fail to "respond for causing said fre'sultant wave tobe applied' to said out put terminals' -to "provide" carrier currents for communication -'passiri g' "between"said input and 'outpiit terminals. 1 I

-BSA frequency selector asclaim'ediniclaim '2' 1n 'whicha change overdevice' is"'pr'o'vided for transferring the control by the; impulses for the first stepping switch" "to the seoondf-s'teppin'g '1' l i 7" ,"U'v: 4 Aftequencyeelector for use in a telecommunication sy tem having 'inputterminal's and output terminals; and i c'o mprisingfla' first series of s'o'u'rces "of fixed frequency 'wavesy the' sources 'o'f said first series beingdesigne'd to supply waves having distinctive frequencies which are "separated by "amounts of one value, "a second ser-i'es sourc -or fixedffrequency waves; the waves or 'said second series being designed" to-supply waves having distinctive frequencies which are separated by amounts of another value, the amount between the lowest and highest frequency of said second series of sources being less than any amount separating the frequencies of said first series of sources, a first wave mixing means, a first selecting device, a first control means connected to said input terminals for effecting the operation of said first selecting device to connect one of said first series of sources to said mixing means, a second selecting device, a change-over device operable when the operation of the first selecting device is completed, a second control means connected to said input terminals by said change-over device for effecting the operation of said second selecting device to connect a predetermined one of said second series of sources to said mixing means, filter means connected to the outlet of said first mixing means to select therefrom a wave of asingle resultant frequency, which frequency is a distinctive combination of the frequency of the waves selected by said switching devices, a second wave mixing means to which the outlet of said first mixing means and the output terminals are connected, wave responding means controlled from said second wave mixing means, which responding means operate when the said resultant Wave and a wave present on said output terminals cooperate to provicle a Wave having a frequency of a given value, a third series of sources of said frequency waves each having distinctive frequencies separated by amounts of a third value and means controlled by said wave responding means for causing said third series of sources to be selected successively, a third mixing means by which the waves are successively applied to said first mixing means to cause the frequency of the resultant Wests; se-zehaneed: within the est'of saidi amounts by? whibh frequenoiesF-of said second series-06f frequencies amseparated until the. wave'wrespbndingmreanss ce'ases ,tciop 'fate: m'ans sresponsi've to the cessation ofsaid selecting?in'eans'tmnause-the resultant wave to be'T'nppliedWo' theacommunicatiomchannel and means responsive to the cessation of operation of isaid wave responding means-to'causethe final resultant wave to lieapplied to said output terminals to provide carrierjeurrents for communications passing between said input and outputrtermina lsne 1 uri- .5. In a telecommunicaticnisyfil fi afrequency selector having input and output terminals com' ,prising'a source ,fproyiding waves of afdistinc; tivefrequency', *fir'st; SBIlBS'O'PSOHIQGSOf 1i d frequency wayesy' a iseconds-series :Qf-fsoure fixed ;::frequenc y=-*-waves,- wave 1- mixing =means,-,a -first, smpulse rcSpon'siye device controllable frgm said input termirials' by:which-:one o f the;source s fromjs'aid first}: series -is-connected-;toj said mix: n "m ans, a secohdy ls SDQ Q erice byiwh-ich onev 10f] "the sources-from said second series; is iconnectedg to-said--mixing means,1 ar;id

filternieans"connected-to the outlet of said mixer by WhiQhLiB ,wayaaofgaresultam single frequency, is derived from, said selected sgurces, connectin means-b which th sai es tanl wave,isl caused gto,,qooperate witlgyz aves preesented to said output terminals, a wave responsive device arranged to respond when the said resultant wave and a wave presented to said output terminals cooperate to produce a wave having a frequency of a given value and means operable if said wave responsivedevice fails to operate to cause the final resultant wave to be applied to said output terminals to provide carrier currents for communications passing between said input and output terminals.

6. A frequency selector as claimed in claim v5 comprising a third series of fixed frequency sources and automatic switching means operated by said wave responsive device if a wave is present on the output terminalswhich in cooperation with said resultant frequency produces a Wave having a frequency of a given value to bring about the generation of waves of resultant frequencies of progressively changing values until a resultant wave frequency is produced not having such a cooperation with waves on the output terminals.

GUY FFARINGTO-N BELLAIRS. JOHN CHARLES IRELAND.

References Cited in the file of this patent UNITED STATES PATENTS 

